Check digit calculator

ABSTRACT

A modulo ten type check digit calculator. It stores the 10 numerals zero through nine and displays only one of them at a time. After manipulation according to the modulo 10 formula with respect to a given number, the numeral displayed represents the check digit for that given number.

I United States Patent 1191 Rapp Dec. 11, 1.973

[ CHECK DIGIT CALCULATOR OTHER PUBLICATIONS [76] Inventor: g g A g i g S tahl & Lettieri, IBM Technical Disclosure Bulletin, L5 n cw or Modulo-l0 Self-Checking Number System, Vol. 7, 0017 N0. 11, April 1965, pp. 1,046-48. 22 mm; 29, 1971 Jay Smith Inc., PCA Check Digit Calculator, Brochure dated 92368. [2]] Appl No.: 213,461

Primary ExaminerCharles E. Atkinson [52] US. Cl... 340/1461 AJ, 235/61 A, 235/6l.7 A Attorney-Th0mas H. Whaley et al. [51] Int. Cl. G06f ll/10 [58] Field of Search 340/l46.l AJ;

235/61 A, 61.7 A [57] ABSTRACT A modulo ten type check digit calculator. It stores the [56] Ref ren s Cit d 10 numerals zero through nine and displays only one UNITED STATES PATENTS of them at a time. After manipulation according to the I 3 modulo 10 formula with respect to a given number, 5:233? the numeral displayed represents the check digit for hat given number. 2,886,240 5/l959 Llnsmen 340/l46.l AJ 2,950,048 8/1960 Luhn 235/6! A 3,45l,6l9 6/1969 Buck 235/6! A 9 Chums 7 Drawmg figures 3,448,254 6/1969 Vcrhoeff 340/l46.l AJ

72 will 1 Bl STABLE MULTIVIBRATOR INPUT DIAL MECHANISM PATENTEBUEBI Y m BJYBJSS sum 1 BF 3 FIG. 1

|' CHECK men CALCULATOR PATENTED DEC? 1 I973 1 CHECK DIGIT CALCULATOR BACKGROUND OF THE INVENTION provide a check digit that is mathematically related to the accound number itself. It is useful in avoiding errors during key-punch machine operations, and the like.

Furthermore, it is often desired to determine what the check digit will be for a given account number, without entering that accound number into the computer. But, in order to do so, the mathematical steps must be carried out and this is time consuming as well as subject to mistakes. The latter is especially true where the person making such calculation does not understand the formula.

A known system for determining one of the foregoing check digits for a given number is commonly known as a modulo type system. Such type of check digit is quite commonly employed with computer listings, and the formula that is applied to make the determination is well known. Also, its use has become standard practice.

Heretofore, there has been proposed a check digit calculator for determining such a check digit, but that proposal employed apparatus that had various drawbacks. Not the least of the drawbacks was the necessity for employing two separate indicia for use alternatively during the process of calculating a check digit. Consequently, that prior apparatus was subject to errors in its use and the reliability was not much of an improvement over the mental process. Such difficulties are substantially overcome by this invention.

Consequently, it is an object of this invention to provide apparatus for calculating a standard modulo 10 type check digit using relatively simple and quite foolproof manipulation of the calculator apparatus.

SUMMARY OF THE INVENTION Briefly, this invention concerns a check digit calculator for use with a standard modulo 10 check digit system. It comprises, in combination, means for storing the 10 numerals 0 through 9, and means for displaying only one of said numerals at a time. It also comprises means for selecting that one of said numerals which represents the modulo-ten check digit of a given whole number, by manipulating said display means in accordance with said modulo l0 formula as applied to said given whole number.

Again briefly, this invention concerns a check digit calculator for use with a standard modulo 10 type check digit system. It comprises, in combination, a flat body member having a face plate, and a disk mounted for rotation behind said face plate. It also comprises an arcuate opening in said face plate concentric with said disk, and a single numeral-sized window in said face plate located diametrically across from said arcuate opening. The numbers 1 through 9 are spaced arcuatedly in equal angular intervals on one side of said arcuate opening and form an add scale on said face plate. The numbers 1 through 9 are spaced arcuately at twice said equal angular interval from one another, and are located radially aligned with various of said add-scale numbers but on the other side of said arcuate opening. The latter form a multiply scale. There are check digit numerals 9 plus 0 located on said disk and spaced on a concentric arc with equal angular intervals as said add-scale numbers, and they are situated for individual display through said window. The invention also comprises 18 depressions on said disk. They are located on a concentric are for coinciding with said arcuate opening, and they are arcuately spaced apart at equal angular intervals which are equal to the intervals of said add scale. Also there is a colored background strip for half of said depressions in order to indicate when the direction of rotationg said window should be reversed. The said arcuate opening extends circumferencially an angular amount such that a single add-scale angular interval of rotating of said disk may be added at either end of said add scale by manipulation using the end one of said depressions opposite the l or the 9 of said add scale.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and benefits of the invention will be more fully set forth below in connection with the best modes contemplated by the inventor of carrying out the invention, and in connection with which illustrations are provided in the drawings, wherein:

FIG. 1 is a plan view showing a manual disk type calculator according to the invention;

FIG. 2 is a plan view showing the face of the rotatable disk element employed with the calculator shown in FIG. 1;

FIG. 3 is a perspective view of the complete calculator according to FIG. 1;

FIG. 4 is a schematic circuit diagram illustrating the elements employed with an electronic embodiment of the invention;

FIG. 5 is a circuit diagram illustrating a multivibrator which may be employed in the system of FIG. 4;

FIG. 6 is a circuit diagram illustrating a diode matrix that may be employed in the FIG. 4 system; and

FIG. 7 is a front elevation, illustrating one physical embodiment of a calculator according to the FIG. 4 system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In present-day business practices where computers are employed for identifying a series of different accounts, it is standard practice to provide a check digit that is mathematically generated by a known formula to assist in avoiding errors such as those made by keypunch machine operators. In addition, it is often extremely helpful to determine the correct check digit for a given new account number before it is entered into a computer.

It will be understood also that it is standard practice to have a computer programmed to generate its own check digit whenever a new account number is entered. The type of check digit thus employed and to which this invention applies, is known as a modulo 10 check digit. The formula for generating such a check digit makes use of the following procedure: Starting with the units digit of an account number, it is doubled (or multiplied by two) and the resulting number is accumulated with the proviso that if the resulting number is 10 or greater, the two digits of such number are added together and accumulated. Then, the next-higher digit of the account number is added to the prior accumulated number and, thereafter, the process is repeated with alternate multiplying and adding the subsequent digits of the account number throughout. Finally, the tens complement of the resulting total is used as the check digit for the particular account.

The foregoing procedure is readily accomplished without convern for the individual arithmetic steps, by employing simple manual manipulation of a calculator according to this invention. It may take various forms. For example, a relatively simple construction is one that employs a rotatable disk in conjunction with a flat plate'on the face of the calculator. Such an instrument is illustrated in the first three figures.

Thus, with reference to FIGS. 1, 2 and 3, there is a flat body member 11 that has located on its face a plurality of arcuate openings 12, 13, and a diamondshape'd opening 14. These are designed to act in conjunction with a rotatable circular disk 17 that is mounted in the body 11 for rotation about its center by means of an axial pin 18. The pin 18 extends through the body 11 from front to back and passes through a complementary sized hole 19 in the disk 17. It will be noted that the opening 14 is only large enough to permit a single one of an arcuate groups 20 of numerals I-9 and 0, to show at a-time.

On the top face of disk 17, there are a plurality of depressions 21. These are 18 in number, and each has a pair of radial lines 22 and 23 associated therewith. In each case the lines 22 and 23 would pass through the center of the depression 21 if extended thereacross. These lines assist in positioning the disk 17 as will appear in more detail hereafter.

There is a colored arcuate shaped strip 26 that surrounds, and acts as background for half of the depressions 21. This strip may be any color, so long as it adequately distinguishes from the background color on the face of the disk 17 which surrounds the other half of the depressions 21. The purpose of this colored strip 26 is to indicate which direction the disk 17 should be rotated for any given multiply or add manipulation.

Also on the front or face of the disk 17, there is the above mentioned series, or group 20, of arcuately positioned numerals one through nine and zero. These numerals 20 are located radially opposite different ones of the depressions 21, and they have an angular or arcuate separation equal to the arcuate spacing between adjacent depressions 21.

It will be observed from FIGS. 1 and 3 that, as the calculator is being used, the numerals on the face of the disk 17 will appear individually one at a time in the opening 14 on the face of the body member 11. Also, for convenience, a word START 29 (FIG. 2) is printed on the face of the disk 17 in such a position as to appear in the opening 13 when the disk is in its starting position, which is that illustrated in FIGS. 1 and 3.

Printed on the face of the body member 11, there are two separate scales 32 and 33 that are made up of the numerals one through nine placed in a manner to be more fully described below. These numerals are located radially in conjunction with radially positioned short lines 34 and 35, respectively, that assist in lining up the depressions 21 opposite particular ones of the numerals. The innermost scale 33 is that employed with the above-described multiply step, while the outer scale 32 is for use with the add" step. To help indicate this, there is a caption MULTIPLY alongside the inner scale 33, and another caption ADD beside the other scale 32.

In addition, there are a pair of arrows 38 and 39 that are associated with the ADD caption, as well as a similar pair of arrows 40 and 41 associated with the MULTIPLY caption. These arrows are preferably printed in two different colors.

The color of arrows 39 and 41 is preferably the same as the color of the background strip 26. It will be noted that this provides a ready indication concerning the direction in which the disk should be rotated for any given manipulation. Thus, whenever a depression 21 that is located within the strip 26 is to be employed for rotating the disk, the disk will be rotated in the direction of the arrows 39 or 41. The opposite holds true for depressions 21 that are outside of the color strip 26, i.e., whenever the other depressions 21 are to be employed, the disk will be rotated in the direction of the arrows 38 or 40.

It will be observed that the numerals 1 through 9 of the outer scale 32 are spaced arcuately at equal angular intervals from one another, all on one side of the opening 12. The other scale 33 has the numerals similarly spaced apart in the numerical order, but at twice the angular interval between the depressions 21. Thus, the numeral one on scale 33 is opposite numeral two on scale 32, and so on through numeral four opposite numeral eight. Then back at the lower end, numeral five on scale 33 is opposite numeral one on scale 32, and thereafter continuing at double intervals with numerals six, seven, eight and nine opposite the numerals three, five, seven and nine, respectively.

Operation of FIGS. 1-3

To illustrate the manner of operating a calculator according to FIGS. 1 and 3, a nine-digit account number such as 342170193 may be employed as an example. Following the above-indicated formula, the calculator must first be set to the start position, which, is illustrated in FIGS. 1' and 3. Then, beginning with the units digit of the foregoing accound number, the number three is to be doubled (or multiplied). For thisstep, a pencil eraser or the like will be placed in the depression 21 opposite the numeral three on the multiply scale 33. Then, the pencil is moved downward until it stops at the lower edge of the opening 12. This carries out the first step since the disk 17 will have been rotated through an arc equal to six of the arcuate spacings between depressions 21.

Next, the formula calls for adding the second digit which, in the illustrated case, is number nine. To accomplish this, the pencil eraser will be placed in the depression 21 that is located opposite the numeral nine on the add scale 32. Since the red strip 26 will have been rotated down past the number nine position by the previous step, the manipulation called for is indicated by the red-colored arrow 39. Therefore the disk will be rotated upward (as viewed in FIGS. 1 and 3) for one arcuate interval.

The next step is a multiply step again, and the number in the above example is number one so that the pencil will be placed into depression 21 that is standing opposite the numeral one of the scale 33. The disk 17 is then rotated downward (for two intervals) in the direction of the arrow 40.

Continuing, the next step called for is that of adding a zero, which is the next digit of the account number of this example. To accomplish this nothing is manipulated. Rather, the add step will be skipped.

Then, the next digit in the example is a seven and the step is multiply so that the same procedure will be followed as in the first and third steps. Thus, using the depression 21 that is located opposite the numeral seven on the multiply scale 33, and rotating the disk 17 in the direction indicated by the red arrow 41, the disk is moved upward so as to accumulate the doubled quantity relating to the digit seven.

The foregoing alternate adding and multiplying continues in like manner with the remaining digit numbers I, 2, 4 and 3 of the example. The final check digit that appears in the opening 14 when the last manipulation has been completed, is the numeral three of the group 20 of numerals on the disk 17. This three, then, represents the check digit for this account number, and it is the tens complement of the accumulated sum of the different numbers, all in accordance with the abovedescribed formula.

Electrical Embodiment FIGS. 4 through 7 illustrate an embodiment of the invention that employs electrical and electronic elements. It can accomplish the same modulo 10 type of check digit calculation, and it employs a telephone-dial type of input manipulation. One physical embodiment of such a calculator is illustrated in FIG. 7, and a complete system is shown by the schematic diagram illustrated in FIG. 4.

It will be understood that various different designs or other structural arrangments will suggest themselves to one skilled in the art. However, the illustrated embodiment that is shown in FIG. 7 includes a base element 51 that supports an upper housing 52 as well as a numeral display panel 53. Panel 53 is situated above the housing 52 and it is attached by means of any feasible structural arrangement, e.g., by having a'support arm 56 connecting the panel 53 with the housing 52. On the front of the housing 52, there is a telephone-dial type of disk 57 that has nine finger holes 58 therein for manipulating the disk in rotating about its center. There is also a finger stop arm 61 which-is like the ordinary telephone dial arrangement.

As will appear in more detail hereafter, the structural arrangement including the dial disk 57 is a modified telephone dialing system. It is constructed so that whenever the disk 57 is rotated by finger manipulation, it acts against a return spring (not shown) to take the disk back to its original position, i.e., that illustrated in FIG. 7. At the same time, the mechanism employs a ratchet coupling (not shown) so that a contact arm 64 (FIG. 4) is rotated a given number of angular steps, depending upon which of the finger holes 58 is employed in ma nipulating the dial 57.

It will be observed that there are located on the face of the housing 52, two series of indicator lights 65 and 66. They are placed radially in line with the nine finger holes 58 ofthe disk 57. As will appear in more detail hereafter, these two series of lights 65 and 66 are alternatively illuminated, and they are marked with the numerals one through nine in the manner illustrated in FIG. 7. Thus, the series 65 has the numerals in numerical order, while series 66 follows the position and number order that is comparable to the multiply scale 33 of the FIGS. 1-3 modification. In addition, there is a pushbutton type switch 69 which has a numeral zero printed on the housing 52in order to indicate that it is to be operated whenever a zero digit is encountered in an account number during a given check digit calculation.

Located on the base 51, there is a switch 72 for turning on and off the power supply to the calculator. Also, there is a group of three indicator lights 74, 75, and 76. These are employed to provide indications concerning the operating state of the system as it is in use. Preferably, the light 74 is a distinct color such as red, while lights 75 and 76 may be green.

FIG. 4 is a schematic diagram showing the entire system according to this modification. It will be noted that there is a pair of input terminals 80 to which there are connected two transformers 81 and 82 in parallel. The switch 72 is connected into one side of the line for controlling energization of the system. The outputs from transformers 81 and 82 are connected in series to the input of a full-wave rectifier bridge 85 which has its output filtered to remove ripple. The filter includes a capacitor 86 that is connected across the output of the bridge 85. One side of capacitor 86 is connected to ground via a circuit connection 88 and a grounding connection 87, as'illustrated.

There is a bi-stable multivibrator 90 that is energized with DC from the output of the rectifier 85, via a circuit that includes a connection 91 (FIGS. 4 and 5). The multivibrator 90 acts to control a relay 92 (FIG. 5), which has a coil 93. When the relay, i.e. coil 93, is energized it will position a movable contact 94 from the position illustrated in FIG. 5, to the opposite position.

The multivibrator may be a standard circuit such as that illustrated in FIG. 5. It employs two crossconnected transistors 96 and 97 which act in a wellknown manner so that no detailed description is necessary. The operation is such that in one of the two bistable states, transistor 96 will be conducting and, consequently, coil 93 of relay 92 will be energized. This means that the movable switch contact 94 of a doublethrow switch 100 will be in the opposite position from that illustrated. Consequently it will complete a circuit between a common circuit connector 101 and a connector 102.

On the other hand, when the multivibrator is in the opposite stable state, transistor 97 will be conducting and, consequently, transistor 96 will not be conducting any longer. Therefore the relay 92 will be returned to the position illustrated in FIG. 5. Consequently, an alternative circuit will be completed from the common connector 101 to another connector 103. It may be noted that the alternative circuits controlled by the switch contact 94 of the switch 100 of the relay 92, will energize one or the other of the series of lights 65 or 66, in addition to the one or the other of the indicator lights 74 or 75 therewtih, respectively.

In FIG. 4, there is a block-diagram type of showing for an element 107. This element 107 represents the telephone dial mechanism which was generally described above in connection with FIG. 7. It is to be noted here that this mechanism includes a mechanism 109 (schematically indicated by dashed line) that is for actuating a normally closed switch 108. Switch 108 is opened each time the telephone-dial disk 57 (FIG. 7) is manipulated. In series with the switch 108, there is the zero switch 69 that is a normally closed pushbutton type. Both of these two switches act individually when either is opened to cause a change-over of the multivibrator from one stable state to the other. i

As already indicated above in connection with the description of FIG. 7, there is a rotatable contact arm 64 (FIG. 4) that is rotated in steps from one through nine depending upon which of the finger holes 58 is chosen. The rotation is always in the same direction and there are ten different positions which may be the final resting place for the arm 64. In conjunction with the final resting positions for the contact arm 64, there are a plurality of stationary contacts 111 in number). These contacts are individually selected by the position of the contact arm 64. As shown in FIG. 4, the contacts 111 are connected into a diode matrix 112 which has output connections 113, as shown (FIGS. 4 and 6), leading to each of seven numeral-indicating bars, or lights 115. These lights 115 will be energized in predetermined combinations so as to provide the indication for a particular numeral from zero through 9, depending upon which of the stationary contacts 111 has been selected by the arm 64.

The details of the circuit for the diode matrix 112 are illustrated in FIG. 6. It will be understood that by the proper interconnection of a plurality of diodes 117, there will result a predetermined combination of energized circuits over selected ones of the connections 113, to energize the indicator bars, or lights 115 that are selected. Thus, for example, when a circuit connection 119 (FIG. 4) is completed by the arm 64, it will energize two circuits in parallel. One is a circuit to illuminate the indicator light 76 and the other will energize a circuit connection (FIGS. 4 and 6) that is shown as the lowermost wire of the left-hand circuit wires illustrated in FIG. 6. By tracing the circuits that are energ'ized via the diodes 117, it may be observed that the outermost six bar lights 115 will'be energized, but not the middle horizontal bar. Consequently, the numeral zero will be illuminated on the panel 53.

Operation of FIGS. 4,.7 Modification In light of the above description relating to the FIGS. 1 and 3,'it will be clear to one skilled in the art that the same basic concepts are involved in operating the electr'ical and electronic modification illustrated in FIGS. 4-7. However, a difference in the manipulation involves the mechanics of the arrangement which relates to the telephone-dial structure.

As indicated previously, the contact arm 64 is always rotated only in one direction and for a given number of angular steps. Also, the separate groups of digit numeral indicating lights 65 and 66 correspond to the add" and multiply scales 32 and 33 of FIGS. 1-3, respectively. Consequently the manipulation in order to carry out the modular ten type check digit formula is substantially similar to that of the hand-disk model (FIGS. 1-3), but is somewhat simplified. The telephone dial disk 57 is always rotated in one direction only and it automatically returns to the starting position (illustrated in FIG. 7) thereafter.

In order to carry out the steps according to the formula, the system will be first set to a starting position by dialing in the same number as that then appearing on the panel 53. That will automatically set the contact arm 64 to the zero position ane consequently light up the combination of bar lights 115 that are shown in solid lines in FIG. 7, which indicates a zero on the panel 53.

Thereafter, commencing with the first digit of an account number, the finger hole 58 opposite the corresponding number of the lighted series of lights 66, will be the one employed to dial in the multiply" step for that digit. When this has been done, the other series of lights will be illuminated while the series 66 will not. Consequently, at the next manipulative step in the formula, the next digit of the account number will be selected from the lighted series 65 and dialed in as before. This will cause the ADD accumulation that follows the earlier doubling of the MULTIPLY step.

Each time such dialing is carried out, the switch 108 is opened during the dialing action. Consequently, the multivibrator is switched over to its opposite state. This is what controls the alternate illumination of the series of lights 65 and 66 so that each step will employ the proper series of numbers as the input.

It may be noted that the switches 108 and 69 are in series in the DC power supply for the multivibrator 90. The plus voltage side is fed over the connection 91 and then via another connection 123 to one side of the switch 108. Then from the remote side of the other switch 69, there is a connection 124 back to plus voltage circuits in the multivibrator. Consequently, whenever either of these switches is opened, the powersupply is temporarily removed and this causes the multivibrator to switch over to the opposite state.

Whenever a zero digit in the account number is encountered, the push-button switch 69 will be activated. This will cause switching of the multivibrator to the opposite state and light the other group of lights 65 or 66. Consequently the system is readied for the next step in the formula manipulations.

While particular embodiments of the invention have been described above in considerable detail in accordance with the applicable statutes, this is not to be taken as in any way limiting the invention but merely as being descriptive thereof.

What I claim is:

1. Check digit calculator for use with a standard modulo ten type check digit system, comprising in combination means for storing the 10 numerals 0 through 9,

means for displaying only one of said numerals at a time, and

means for selecting that one of said numerals which represents the modulo-l0 check digit of a given whole number by manipulating said storing means relative to said display means in accordance with said modulo-l0 formula as applied to said given whole number, which comprises means for alternately doubling and adding the individual digits of said given whole number taken in sequence,

said doubled digits 5 through 9 being represented by the sum of the digits of the double quantity,

said numeral representing the check digit being the tens complement of the alternately accumulated total.

2. Check digit calculator according to claim I, further comprising a face plate,

a disk mounted for rotating behind said face plate,

.and

wherein said storing means comprises said numerals printed on said disk, and wherein said displaying means comprises a window in said face plate.

3. Check digit calculator according to claim 2, wherein said means for alternately doubling and adding comprises separate scales marked on opposite sides of an arcuate opening in said face plate, and said disk has an arcuate series of depressions concentric with said arcuate opening, said depressions being radially aligned wiith said scale markings. I 4. Check digit calculator according to claim 3, wherein said add scale comprisesnumbers one through nine spaced arcuately at equal intervals, and said doubling scale also comprises numbers one through nine but spaced arcuately at double said add-scale intervals, said depressions being 18 in number with one half being marked to be readily distinguishable from the other half, said arcuate opening extending one of said add-scale intervals beyond the ends of said add-scale numbers. 5. Check digit calculator according to claim 4, wherein said disk numerals are arranged in inverse numerical order relative to said add-scale numbers and spaced arcuately at equal intervals that are arcuately equal to said add-scale intervals. 6. Check digit calculator according to claim 1, wherein I said storing means comprises a diode matrix, said displaying means comprises a group of illuminable elements for forming said numerals by being illuminated in different combinations, and wherein said alternate doubling and adding means comprises a rotatable switch having 10 positions equally spaced around a radial contact arm, means for moving said arm in one direction of rotation only in steps of 36 or whole multiples thereof, circuit means for connecting said switch positions to said matrix, alternately selectable doubling and add scales corresponding with nine of said ten switch positions, said add scale comprising the numbers one through nine consecutively indicating said nine switch postions, and said doubling scale comprising the numbers one through nine indicating sequentially the same switch positions as the add-scale numbers two, four, six, eight, one, three, five, seven and nine respectively, all whereby said rotatable switch may be manipulated in steps as determined by said alternately selectable scales and in accordance with said modulo-l formula. 7. Check digit calculator according to claim 6, wherein said alternate doubling and adding means further comprises means for indicating which of said alternate scales should be employed during said modular ten formula procedure, and a zero switch with circuit means for shifting said indicating means to the opposite scale when a zero digit is encountered in said given whole number. 8. Check digit calculator according to claim 1, wherein said storing means comprises a plurality of contacts on a rotary switch, and said displaying means comprises a group of illuminable elements for forming said numerals by being illuminated in different combinations, and wherein said alternate doubling and adding means comprises a rotatable switch arm for contacting said contacts individually,

means for moving said arm in one direction only in steps of 36 or whole multiples thereof,

circuit means including a diode matrix for connecting said contacts to said illuminable elements, and

alternately selectable doubling and add scales corresponding with all except one of said contacts,

said add scale comprising the numbers one through nine consecutively indicating nine of said contacts, and

said doubling scale comprising the numbers one through nine indicating sequentially the same contacts as said add-scale numbers two, four, six, eight, one, three, five, seven, and nine respectively,

all whereby said rotatable switch arm may be manipulated in steps as determined in accordance with said alternately selectable scales and in accordance with said modulo-ten formula.

9. Check digit calculator for use with a standard modulo-ten type check digit system, comprising in combination a flat body member having a face plate,

a disk mounted for rotation behind said face plate,

an arcuate opening in said face plate concentric with said disk,

a single numeral-sized window in said face plate located diametrically across from said arcuate opening,

numbers one through nine spaced arcuately at equal angular intervals on one side of said arcuate opening and forming an add scale on said face plate,

numbers one through nine spaced arcuately at twice said equal angular interval from one another and located radially aligned with various of said addscale numbers but on the other side of said arcuate opening and forming a multiply scale,

check digit numerals one through nine plus zero located on said disk and spaced on a concentric arc with equal angular intervals as said add-scale numbers and being situated for individual display through said window,

18 depressions on said disk located on a concentric are for coinciding with said arcuate opening and being arcuately spaced apart at equal angular intervals equal to the intervals of said add scale, and

a colored background strip for one half of said depressions in order to indicate when the direction of rotation of said disk should be reversed,

said arcuate opening extending circumferentially an angular amount such that a single add-scale angular interval of rotation of said disk may be added at either end of said add scale by manipulation using the end one of said depressions opposite the one or the nine of said add scale, all whereby said disk may be manipulated using said depressions in conjunction with said multiply and add scales plus said colored strip and in accordance with said moduloten formula. 

1. Check digit calculator for use with a standard modulo ten type check digit system, comprising in combination means for storing the 10 numerals 0 through 9, means for displaying only one of said numerals at a time, and means for selecting that one of said numerals which represents the modulo-10 check digit of a given whole number by manipulating said storing means relative to said display means in accordance with said modulo-10 formula as applied to said given whole number, which comprises means for alternately Doubling and adding the individual digits of said given whole number taken in sequence, said doubled digits 5 through 9 being represented by the sum of the digits of the double quantity, said numeral representing the check digit being the tens complement of the alternately accumulated total.
 2. Check digit calculator according to claim 1, further comprising a face plate, a disk mounted for rotating behind said face plate, and wherein said storing means comprises said numerals printed on said disk, and wherein said displaying means comprises a window in said face plate.
 3. Check digit calculator according to claim 2, wherein said means for alternately doubling and adding comprises separate scales marked on opposite sides of an arcuate opening in said face plate, and said disk has an arcuate series of depressions concentric with said arcuate opening, said depressions being radially aligned wiith said scale markings.
 4. Check digit calculator according to claim 3, wherein said add scale comprises numbers one through nine spaced arcuately at equal intervals, and said doubling scale also comprises numbers one through nine but spaced arcuately at double said add-scale intervals, said depressions being 18 in number with one half being marked to be readily distinguishable from the other half, said arcuate opening extending one of said add-scale intervals beyond the ends of said add-scale numbers.
 5. Check digit calculator according to claim 4, wherein said disk numerals are arranged in inverse numerical order relative to said add-scale numbers and spaced arcuately at equal intervals that are arcuately equal to said add-scale intervals.
 6. Check digit calculator according to claim 1, wherein said storing means comprises a diode matrix, said displaying means comprises a group of illuminable elements for forming said numerals by being illuminated in different combinations, and wherein said alternate doubling and adding means comprises a rotatable switch having 10 positions equally spaced around a radial contact arm, means for moving said arm in one direction of rotation only in steps of 36* or whole multiples thereof, circuit means for connecting said switch positions to said matrix, alternately selectable doubling and add scales corresponding with nine of said ten switch positions, said add scale comprising the numbers one through nine consecutively indicating said nine switch postions, and said doubling scale comprising the numbers one through nine indicating sequentially the same switch positions as the add-scale numbers two, four, six, eight, one, three, five, seven and nine respectively, all whereby said rotatable switch may be manipulated in steps as determined by said alternately selectable scales and in accordance with said modulo-10 formula.
 7. Check digit calculator according to claim 6, wherein said alternate doubling and adding means further comprises means for indicating which of said alternate scales should be employed during said modular ten formula procedure, and a zero switch with circuit means for shifting said indicating means to the opposite scale when a zero digit is encountered in said given whole number.
 8. Check digit calculator according to claim 1, wherein said storing means comprises a plurality of contacts on a rotary switch, and said displaying means comprises a group of illuminable elements for forming said numerals by being illuminated in different combinations, and wherein said alternate doubling and adding means comprises a rotatable switch arm for contacting said contacts individually, means for moving said arm in one direction only in steps of 36* or whole multiples thereof, circuit means including a diode matrix for connecting said contacts to said illuminable elements, and alternately selectable doubling and Add scales corresponding with all except one of said contacts, said add scale comprising the numbers one through nine consecutively indicating nine of said contacts, and said doubling scale comprising the numbers one through nine indicating sequentially the same contacts as said add-scale numbers two, four, six, eight, one, three, five, seven, and nine respectively, all whereby said rotatable switch arm may be manipulated in steps as determined in accordance with said alternately selectable scales and in accordance with said modulo-ten formula.
 9. Check digit calculator for use with a standard modulo-ten type check digit system, comprising in combination a flat body member having a face plate, a disk mounted for rotation behind said face plate, an arcuate opening in said face plate concentric with said disk, a single numeral-sized window in said face plate located diametrically across from said arcuate opening, numbers one through nine spaced arcuately at equal angular intervals on one side of said arcuate opening and forming an add scale on said face plate, numbers one through nine spaced arcuately at twice said equal angular interval from one another and located radially aligned with various of said add-scale numbers but on the other side of said arcuate opening and forming a multiply scale, check digit numerals one through nine plus zero located on said disk and spaced on a concentric arc with equal angular intervals as said add-scale numbers and being situated for individual display through said window, 18 depressions on said disk located on a concentric arc for coinciding with said arcuate opening and being arcuately spaced apart at equal angular intervals equal to the intervals of said add scale, and a colored background strip for one half of said depressions in order to indicate when the direction of rotation of said disk should be reversed, said arcuate opening extending circumferentially an angular amount such that a single add-scale angular interval of rotation of said disk may be added at either end of said add scale by manipulation using the end one of said depressions opposite the one or the nine of said add scale, all whereby said disk may be manipulated using said depressions in conjunction with said multiply and add scales plus said colored strip and in accordance with said modulo-ten formula. 